The present invention relates to arranging traffic within telecommunication equipment and internal traffic between a plurality of telecommunication equipment. In particular, the invention relates to internal traffic in a node of a broadband telecommunication network, such as an ATM node.
The architecture of a modern digital exchange is illustrated in FIG. 1. The basic function of the exchange is to connect the exchange input port to the correct output port, in other words, to connect an incoming call on a specific incoming circuit to an outgoing call on a specific outgoing circuit. In practice, the information in a specific input side PCM timeslot is connected to a specific PCM timeslot at the output side. The incoming circuits, whether backbone lines or subscriber lines, are connected to the exchange by line interfaces. A switching matrix interconnects incoming and outgoing speech channel timeslots, and also the signalling channels and internal data channels of the exchange are connected through it.
The core of the system is the exchange control whose functions have been distributed over a plurality of units, denoted in the figure with general reference marks Unit 1, . . . , Unit N, each carrying out its own task. As examples of such units are mentioned a unit controlling the switching matrix, signalling units carrying out different types of signalling and supervision at the input and output sides, a unit collecting call-specific charging data, a unit gathering statistics, etc. Each unit comprises at least one central processing unit CPU, a bus adapter and memory. Thus, each unit actually constitutes a computer.
The units must be able to negotiate with each other, so this exchange-internal traffic has to be arranged in some way. The most common way is to set up a dedicated common message bus, as done in, FIG. 1, into which the units are connected via the bus adapter. Also, the data transmitted by the exchange units to units of another exchange can be considered to be internal traffic. A typical example of this are the various types of messages exchanged in connection with the call set-up phase. Therefore, depending on the case, the common resources shared by internal traffic are the message bus, switching stage and the trunk circuits between nodes.
The exchange additionally comprises an Operation and Maintenance Unit (OAM), taking care of the maintenance of the system.
This prior art architecture is based on the use of a common message bus which carries traffic between the units. The main part of that traffic thus passes isolated from the other traffic passing through the exchange. The exchange switching matrix connects the signalling messages sent by the nodes to other nodes, to the appropriate circuit and correspondingly the switching stage forwards the messages received from the circuits for this node to the correct units.
Apart from the type described above, the telecommunication network nodes may also be ATM nodes (Asynchronous Transfer Mode), as is nowadays the case more and more often. ATM is a connection-oriented, packet switched, general purpose and scalable data transmission method in which information is sent in fixed-length cells. The cell consists of a five-byte-long header and a 48-byte-long information section. The header fields include a Virtual Path Indicator (VPI) and a Virtual Channel Indicator (VCI). At the ATM switch, the cells are transferred from a logical input channel to one or more logical output channels. The logical channel consists of the number of the physical link (e.g. optical cable) and the channel identifier on this link, in other words the VPI/VCI information. One physical transfer medium, such as an optical cable, may comprise a plurality of virtual paths VP and each virtual path comprises a plurality of virtual channels VC.
Because the cells are of a fixed length, the connections at ATM switches can be performed at equipment level on the basis of the cell header, and therefore at very high speed. Cells belonging to different connections are distinguished from each other on the basis of the virtual path (VPI) and the virtual channel (VCI) identifier. As the connection is set up, a fixed route is determined through the network, i.e. a virtual link along which the cells of the connection are routed. Based on the VPINCI values, the cells are switched at the network nodes. The VPINCI values are transmission link specific and consequently usually change in connection with switching at VP or VC level. At the end of the data transfer, the connection is released.
FIG. 2 illustrates a simplified ATM switch. It consists of input stages and output stages, into which the physical input and output fibres are connected, and of a switching stage. The input and output stages constitute the external network interfaces. The interface type may be either UNI (User Network Interface) or NNI (Network Network Interface). The input stage reads the address information, i.e. VPI and VCI identifiers, of the cell received from the input link and converts them into new VPINCI values which the output stage inserts into the header of the cell sent to the output link. The conversion is carried out with the aid of a conversion table, and at the same time the switching stage is informed of which output link the switching stage is to direct the cell in question.
The software of the switch is distributed over functional blocks, processor units 1, . . . n, handled by computers. The most complex tasks may be left for the central processor to handle. The computers are nearly always of the embedded type, meaning that display units and other peripheral devices are not required.
As the figure indicates, the architecture of the ATM switch greatly resembles that of an STM switch; after all, the basic task of them both is the same, e.g. to connect information from an input link to an output link.
FIG. 3 is a more detailed illustration of an ATM switch. A cell, either of UNI or NNI type, from optical fibre 7 is received at circuit 31 of the PHY layer that terminates the line. The PHY (Physical Layer) carries out transmission system specific tasks at the bit level and is responsible for cell adaptation to each of the transmission systems, as well as for cell masking, cell header error checks, and cell rate justification.
From circuit 31 of the PHY layer, the cell passes to circuit 32 of the ATM layer over the interface. The ATM layer only deals with the cell header, its task being cell switching, multiplexing and demultiplexing, cell header generation and removal, as well as flow control at the User Network Interface (UNI). Additional tasks for the ATM layer include header error detection and correction, as well as block synchronization. Above the ATM layer, the AAL (ATM Adaptation Layer) fragments the higher layer frames and reassembles them at the other end, in other words, carries out the SAR (Segmentation and Reassembly) function.
The above interface has been standardized by the ATM Forum as UTOPIA, and it has become the de facto industrial standard followed by all the manufacturers of integrated ATM circuits. Over the interface, nothing but ATM cell data is transmitted, which includes control signals required by the two-way transfer, i.e. the so-called handshaking signals.
Circuit 32 of the ATM layer sends the cell to the input buffer of ATM switching stage 33. From there, the stage connects it to the other side of the stage, to output port 35. At the output port, the VPI/VCI value in the cell address field is examined, and the cell is transmitted to the correct virtual channel.
The processor units in FIG. 2 and the processor units in other nodes must be able to negotiate with each other. One way to arrange node-internal traffic is to connect the processor units to a common bus, which is done in the case of the switch in FIG. 1.
Another way is to send the internal-traffic cells among other traffic, as illustrated in FIG. 4. Here, the applications of processor units Unit 1, . . . , unit N may directly connect to each other via the AAL/ATM and PHY layers. One of the units (Central Processor) is the control computer controlling the switching stage. Because the processor units are connected to the ATM network as any other traffic source, the applications running in the unit can transmit information to the applications in the other units and receive information from each other. It should be noted that data transfer between applications within the processor unit naturally takes place using the computer""s internal bus. The AAL layer fragments the data produced by the application and intended for an application running in another processor unit to the length of the ATM cell""s data section. The ATM layer packets the data into the ATM cells and adds the VPI/VCI information to them. The physical layer sends the packets forward.
At the virtual connection set-up phase, the source and the network negotiate what kind of behaviour is expected of the ATM layer, i.e. they make a traffic agreement. The source informs the network of its traffic parameters and the Service Category it wants. The characteristics of the source, such as a computer, are described with traffic parameters. Firstly, they are utilized in the Connection Admission Control (CAC) process where the network decides whether the requested connection can be granted, and secondly in association with connection and network parameter supervision where the network element monitors that the source stays within the traffic parameters it has announced.
It has nowadays been agreed that the traffic source requesting a connection at least indicates the following as its traffic parameters: PCR (Peak Cell Rate), SCR (Sustainable Cell Rate), MBS (Maximum Burst Size), MCR (Minimum Cell Rate), and QoS (Quality of Service). Quality parameters include CVD (Cell Delay Variation), MaxCTD (Maximum Cell Transfer Delay) and CLR (Cell Loss Ratio).
The source additionally states the ATM adaptation layer (AAL) service it wants. AAL protocols comprise AAL1, AAL2, AAL3/4 and AAL5. Attached Table 1 shows the ATM layer service categories according to the ATM Forum, and the related traffic parameters.
CBR (Constant Bit Rate) is intended for real-time traffic sources that transmit at a fixed rate. Attributes relating to delay and variation thereof are guaranteed for the connection.
VBR (Variable Bit Rate) is intended for variable rate traffic sources. The category has been divided into two subcategories: rt-VBR, in which rt stands for real time, and nrt-VBR in which nrt stands for non real time. The sources are bursty, which means that the source must announce the Maximum Burst Size MBR.
ABR (Available Bit Rate) is intended for bursty sources that do not have tight constraints on delay variation, which means that no guarantees are given as to transmission delays. The source must announce the Minimum Cell Rate (MCR).
UBR (Unspecified Bit Rate) is intended for delay-tolerant, low-priority traffic.
The use of the network resources is controlled by Traffic Management and Performance Management. Traffic management is based on monitoring the traffic parameters agreed upon at the connection set-up stage, so that a specific Quality of Service guaranteed for the traffic source is maintained.
When cells of switch-internal traffic are transmitted among other traffic, the common resources create the problem that internal traffic can cause interference to other traffic. Interference is caused to subscriber traffic, if internal traffic decreases the quality of service intended for subscriber traffic by, for example, increasing the Cell Loss Ratio of subscriber traffic ATM cells.
The object of this invention is an arrangement according to which the interference caused by internal traffic to other traffic can be minimized while, however, maintaining internal traffic as efficient as possible. The aim is to integrate internal traffic with subscriber traffic and to offer the best possible connection quality for different applications when internal traffic and subscriber traffic use common resources.
This aim is achieved with specifications described in the dependent claims.
The invention is based on the observation that the quality of an internal connection depends on which service category it belongs to. That being the case, it is possible to optimize the quality of the connection services of internal connections by assigning service categories to the applications, which correspond as well as possible to their quality needs. Secondly, by setting the traffic parameters of internal traffic individually changeable, internal traffic and subscriber traffic can be integrated in the best possible way.
In the preferred embodiment, the service category can be selected connection-specifically. In such a case, each application selects the best possible service category.
In the second embodiment, the connection-specific service category is selected to be the same for all the applications. In such a case, all the applications use the same predetermined service category.
In a variation of the second embodiment, the applications are divided into groups, and the same service category is selcted for all the applications within the group. Consequently, the same applications within a group always use the same predetermined service category.